There are many instances in today's information age in which information is communicated wirelessly. Computing devices widely are equipped with radios for the wireless exchange of information with other computing devices. Wireless communication enables a wide range of functionalities to be available through a computing device, without a requirement that the computing device be physically connected to those computing devices or even to a network through which those computing devices can be reached. Rather, mobile computing devices are known to be wirelessly connected to a network, such as the Internet, through which information can be exchanged with other computing devices. Computing devices may also be directly connected to each other or to peripheral devices, such as printers and display devices, through wireless connections. Even for devices that are primarily intended for use in a single location, a wireless connection may be provided to avoid the need to route wires in that location.
In addition, wireless communication is used for purposes beyond interconnecting computing devices. Wireless communication allows audio and video content to be broadcast to multiple receivers. For instance, television signals are often communicated wirelessly. Similarly, audio radio stations also broadcast signals wirelessly. Moreover, wireless communications play an important role in military and public safety related communications. As yet a further example, wireless communication also enables mobile phone services.
To avoid interference between many entities trying to communicate wirelessly, multiple techniques may be used. One technique separates users by frequency such that transmissions by users are made at different frequencies. A device may have a radio tuned to receive communications having a particular frequency characteristic, while excluding other communications.
To accommodate the many entities that desire to use wireless communication, the available frequency spectrum that is usable for wireless communication is divided into domains. These domains are established by government regulators such that different frequencies may be used for different purposes in different countries. However, in all countries it is generally the case that regulations establishing a domain define who is permitted to use the domain and the purposes for which the corresponding frequency band can be used. For example, in the United States, a domain is established for transmission of digital television signals. A separate domain has been established for Industrial, Scientific and Medical (ISM) radios and another domain. Another domain, called the Unlicensed National Information Infrastructure (UNIT) domain, is used for wireless communication in accordance with a widely used standard, the 802.11 standard, for connecting computers wirelessly to local area networks.
Each domain may be assigned a range of frequencies such that, even within the domain, multiple users may communicate using different frequencies. As part of the regulation establishing a domain, a mechanism may be defined by which multiple users share the spectrum allocated for the domain without interfering with one another. In some instances, a domain is licensed, meaning that a specific frequency is assigned to a specific entity, at least within some limited geographic area.
In other instances, though the domain is unlicensed, limitations may be imposed on devices intended to communicate in the domain to avoid interference. For example, maximum power output limitations may be imposed to reduce the likelihood that transmission from one user's device will interfere with another user's device, which is not intended to receive the transmission. As another example, a device attempting to transmit in a particular domain may be required to sense whether a particular set of frequencies is in use prior to using those frequencies.
Despite the establishment of multiple domains, and techniques within each domain to avoid interference, there is a shortage of available spectrum for some uses. Unlicensed computer-to-computer communications and computer-to-peripheral communications are two examples of such uses. To make more frequencies available for such uses, it has been proposed to use unassigned bands of the licensed spectrum, referred to as “white space,” which may exist for any of numerous reasons. For example, when frequency bands of the licensed spectrum are assigned to organizations, typically they are not assigned exactly consecutively; instead, there may be gaps between the licensed portions to prevent two entities from interfering with one another.
In particular, it has been proposed to use white space in the digital television domain for computer (e.g. computer-to-computer, computer-to-peripheral) communications because this spectrum has the advantage of being close in frequency to the frequencies used for computer communications. Also, there may be white space in a geographic region because there are fewer licensed TV stations in that region than the digital TV domain can accommodate. However, because the amount of available white space varies from location to location, such use of the digital TV spectrum is done cognitively, such that a computer determines whether a frequency is already in use, before using it. This determination may be made by a computing device sensing signals to find an unused channel or by consulting a database of licensed channels applicable in the location.